I am sure that Glocks are good guns. I have shot quite a few when I was shopping around. I do not like them much myself, for the following reasons:
1. Cosmetics: Glocks are plug ugly, purely utilitarian. They are also too thick because of all the polymer/double stack mags. I know that beauty lies in the eye of the beholder, so I am only speaking for myself, but Glocks are not handsome guns.
2. Trigger: Feels too "mushy" and releases without a pronounced release point. I am trained to take the slack out of a DA/SA trigger prior to a "deliberate" target shot, and the Safe Action trigger is too much of a switch for my drilled and conditioned trigger finger.
I believe in the philosophy that you should carry what you are used to, and my SIG is like a body extension after a decade of owning SIGs. I know that Glocks are popular and reliable, but they just don't do it for me. For some reason, I don't like any polymer-framed guns, with the exception of the H&K USP...I've never seen a gun come out of their factory that I didn't like.
As some folks say, it's Chevy vs. Ford on this issue. Personally, I think that in the case of Glock vs. SIG it's more like Volkswagen vs. BMW.